Digital Focus: File Formats and Image Compression

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Feature: Mastering File Formats and Image Compression

When it comes to computer technology, there's no such thing as the good old days. In years past, just about everything was more difficult. Take file formats for digital pictures, for instance. There's a smorgasbord of picture file formats available today; but in 1993, you needed special software just to convert pictures from one format to another. Most image editors opened only a few kinds of pictures, and there was no standard format at all.

Of course, that doesn't mean everything is hunky dory today. We've still got a handful of different formats to choose from, and it's not always obvious which one is best. This week, let's talk about the various kinds of file formats and when you might want to use them.

The Problem With JPEG

No doubt you're familiar with the JPEG format, which virtually all digital cameras use by default. And almost any computer in the world can display a JPEG, making it an ideal way to keep and share pictures. The main reason for JPEG's popularity is that the format does a superb job of saving hard drive space. A high-resolution picture with 25MB of color and pixel information in it can be shrunk down to just a megabyte or so in JPEG format; you can store a staggering number of the files on your computer without running out of space.

But JPEG images aren't perfect. The shrinking process degrades your picture by throwing away color details--details that can never be recovered no matter what you do. Bottom line: A JPEG is an approximation of your original image, sort of like a high-tech photocopy. And if you make changes to a JPEG--such as removing red-eye or cropping it--and save the file again, you're just made a copy of a copy, further eroding the image quality. That's why some professional photographers avoid JPEG and work in other formats.

While we're on the subject, you might want to read "Everything You Didn't Know About JPEG."

The TIFF Alternative

While the JPEG format is all about packing high-quality images into as little space as possible, TIFF files are unapologetically huge. That's because no data is ever discarded when working with or saving the files. Not surprisingly, some photographers set their cameras to record TIFFs instead of JPEGs, and then keep images in TIFF format on the PC as well.

Is there a downside? You bet. Pictures from a 6-megapixel camera clock in around 18MB each. That means your camera saves images more slowly; it can't hold as many in memory; and it will fill up your PC's hard drive more quickly.

Then There's RAW

Some cameras also provide the option of using a format called RAW. Actually, there is no RAW standard: Every manufacturer uses its own version of the format. But no matter whether you have a Canon Digital Rebel, Nikon D100, or Olympus e1, the idea behind RAW is the same. RAW files are completely unprocessed, pure data as saved from the image sensor. No color adjustments, white balance, sharpening, and other stuff has been applied. You get the purest possible picture, ready for adjustment on the computer.

TIFFs and JPEGs and RAWs, Oh My!

So what file format should you use? I advise against RAW unless you're a photographer for "National Geographic" magazine. Few among us have the time or inclination to manually correct all of our digital images when the camera would typically do a perfectly acceptable job for you if you'd picked TIFF or JPEG.

As for choosing between TIFF and JPEG, this decision is a little harder--but I'll still side with JPEG most of the time. Yes, JPEG images are imperfect. But most digital cameras and image editors let you choose the JPEG compression level. If you choose low compression, the image quality is high. And with rare exception, a very high quality JPEG is almost indistinguishable from an unmolested TIFF. I set my camera to the highest quality/lowest compression setting and leave it there without exception. On the PC, I always save my images at the highest quality level. In Jasc Paint Shop Pro, that's a quality level of 1. Make sure to double-check your photo editor to make sure you're using the highest level. In Adobe Photoshop Elements, for example, the scale works differently: The best quality is actually 12.

How do you find the image quality settings? Easy. In Paint Shop Pro, when you choose File, Save As from the menu, click the Options button at the bottom of the Save As dialog box. Drag the Compression Factor slider to the highest quality and then save your picture. (Another option, Lossless, isn't very useful because of the very large files it creates.) You only need to do that once; it'll remember your choice. In Photoshop Elements, when you choose Save As to rename a file, you'll see the JPEG Options dialog box after you click the Save button.

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